Aquaporin-4 Reduces Post-Traumatic Seizure Susceptibility by Promoting Astrocytic Glial Scar Formation in Mice

Pentylenetetrazole: A review

Pentylenetetrazole (PTZ), a tetrazole derivative, is commonly used as a chemical agent to induce neurological disorders and replicate the characteristics of human epileptic seizures in animal models. This review offers a comprehensive analysis of the behavioral, neurophysiological, and neurochemical changes induced by PTZ. The epileptogenic and neurotoxic mechanisms of PTZ are associated with an imbalance between the GABAergic and glutamatergic systems. At doses exceeding 60 mg/kg, PTZ exerts its epileptic effects by non-competitively antagonizing GABAA receptors and activating NMDA receptors, resulting in an increased influx of cations such as Na+ and Ca2+. Additionally, PTZ promotes oxidative stress, microglial activation, and the synthesis of pro-inflammatory mediators, all of which are features characteristic of glutamatergic excitotoxicity. These mechanisms ultimately lead to epileptic seizures and neuronal cell death, which depend on the dosage and method of administration. The behavioral, electroencephalographic, and histological changes associated with PTZ further establish it as a valuable preclinical model for the study of epileptic seizures, owing to its simplicity, cost-effectiveness, and reproducibility.

Non-coding RNAs and Aquaporin 4: Their Role in the Pathogenesis of Neurological Disorders

Neurological disorders are a major group of non-communicable diseases affecting quality of life. Non-Coding RNAs (ncRNAs) have an important role in the etiology of neurological disorders. In studies on the genesis of neurological diseases, aquaporin 4 (AQP4) expression and activity have both been linked to ncRNAs. The upregulation or downregulation of several ncRNAs leads to neurological disorder progression by targeting AQP4. The role of ncRNAs and AQP4 in neurological disorders is discussed in this review.

Epidemiology, Risk Factors, and Biomarkers of Post-Traumatic Epilepsy: A Comprehensive Overview

This paper presents an in-depth exploration of Post-Traumatic Epilepsy (PTE), a complex neurological disorder following traumatic brain injury (TBI), characterized by recurrent, unprovoked seizures. With TBI being a global health concern, understanding PTE is crucial for effective diagnosis, management, and prognosis. This study aims to provide a comprehensive overview of the epidemiology, risk factors, and emerging biomarkers of PTE, thereby informing clinical practice and guiding future research. The epidemiological aspect of the study reveals PTE as a significant contributor to acquired epilepsies, with varying incidence influenced by injury severity, age, and intracranial pathologies. The paper delves into the multifactorial nature of PTE risk factors, encompassing clinical, demographic, and genetic elements. Key insights include the association of injury severity, intracranial hemorrhages, and early seizures with increased PTE risk, and the roles of age, gender, and genetic predispositions. Advancements in neuroimaging, electroencephalography, and molecular biology are presented, highlighting their roles in identifying potential PTE biomarkers. These biomarkers, ranging from radiological signs to electroencephalography EEG patterns and molecular indicators, hold promise for enhancing PTE pathogenesis understanding, early diagnosis, and therapeutic guidance. The paper also discusses the critical roles of astrocytes and microglia in PTE, emphasizing the significance of neuroinflammation in PTE development. The insights from this review suggest potential therapeutic targets in neuroinflammation pathways. In conclusion, this paper synthesizes current knowledge in the field, emphasizing the need for continued research and a multidisciplinary approach to effectively manage PTE. Future research directions include longitudinal studies for a better understanding of TBI and PTE outcomes, and the development of targeted interventions based on individualized risk profiles. This research contributes significantly to the broader understanding of epilepsy and TBI.

Research Progress on the Immune-Inflammatory Mechanisms of Posttraumatic Epilepsy

Posttraumatic epilepsy (PTE) is a severe complication arising from a traumatic brain injury caused by various violent actions on the brain. The underlying mechanisms for the pathogenesis of PTE are complex and have not been fully defined. Approximately, one-third of patients with PTE are resistant to antiepileptic therapy. Recent research evidence has shown that neuroinflammation is critical in the development of PTE. This article reviews the immune-inflammatory mechanisms regarding microglial activation, astrocyte proliferation, inflammatory signaling pathways, chronic neuroinflammation, and intestinal flora. These mechanisms offer novel insights into the pathophysiological mechanisms of PTE and have groundbreaking implications in the prevention and treatment of PTE. Immunoinflammatory cross-talk between glial cells and gut microbiota in posttraumatic epilepsy. This graphical abstract depicts the roles of microglia and astrocytes in posttraumatic epilepsy, highlighting the influence of the gut microbiota on their function. TBI traumatic brain injury, AQP4 aquaporin-4, Kir4.1 inward rectifying K channels.

The Role of Aquaporins in Epileptogenesis-A Systematic Review

Aquaporins (AQPs) are a family of membrane proteins involved in the transport of water and ions across cell membranes. AQPs have been shown to be implicated in various physiological and pathological processes in the brain, including water homeostasis, cell migration, and inflammation, among others. Epileptogenesis is a complex and multifactorial process that involves alterations in the structure and function of neuronal networks. Recent evidence suggests that AQPs may also play a role in the pathogenesis of epilepsy. In animal models of epilepsy, AQPs have been shown to be upregulated in regions of the brain that are involved in seizure generation, suggesting that they may contribute to the hyperexcitability of neuronal networks. Moreover, genetic studies have identified mutations in AQP genes associated with an increased risk of developing epilepsy. Our review aims to investigate the role of AQPs in epilepsy and seizure onset from a pathophysiological point of view, pointing out the potential molecular mechanism and their clinical implications.

The Role of Aquaporins in Spinal Cord Injury

Edema formation following traumatic spinal cord injury (SCI) exacerbates secondary injury, and the severity of edema correlates with worse neurological outcome in human patients. To date, there are no effective treatments to directly resolve edema within the spinal cord. The aquaporin-4 (AQP4) water channel is found on plasma membranes of astrocytic endfeet in direct contact with blood vessels, the glia limitans in contact with the cerebrospinal fluid, and ependyma around the central canal. Local expression at these tissue-fluid interfaces allows AQP4 channels to play an important role in the bidirectional regulation of water homeostasis under normal conditions and following trauma. In this review, we consider the available evidence regarding the potential role of AQP4 in edema after SCI. Although more work remains to be carried out, the overall evidence indicates a critical role for AQP4 channels in edema formation and resolution following SCI and the therapeutic potential of AQP4 modulation in edema resolution and functional recovery. Further work to elucidate the expression and subcellular localization of AQP4 during specific phases after SCI will inform the therapeutic modulation of AQP4 for the optimization of histological and neurological outcomes.

LPS-Induced Systemic Inflammation Affects the Dynamic Interactions of Astrocytes and Microglia with the Vasculature of the Mouse Brain Cortex

The Neurovascular Unit (NVU), composed of glia (astrocytes, oligodendrocytes, microglia), neurons, pericytes and endothelial cells, is a dynamic interface ensuring the physiological functioning of the central nervous system (CNS), which gets affected and contributes to the pathology of several neurodegenerative diseases. Neuroinflammation is a common feature of neurodegenerative diseases and is primarily related to the activation state of perivascular microglia and astrocytes, which constitute two of its major cellular components. Our studies focus on monitoring in real time the morphological changes of perivascular astrocytes and microglia, as well as their dynamic interactions with the brain vasculature, under physiological conditions and following systemic neuroinflammation triggering both microgliosis and astrogliosis. To this end, we performed 2-photon laser scanning microscopy (2P-LSM) for intravital imaging of the cortex of transgenic mice visualizing the dynamics of microglia and astroglia following neuroinflammation induced by systemic administration of the endotoxin lipopolysaccharide (LPS). Our results indicate that following neuroinflammation the endfeet of activated perivascular astrocytes lose their close proximity and physiological cross-talk with vasculature, an event that most possibly contributes to a loss of blood-brain barrier (BBB) integrity. At the same time, microglial cells become activated and exhibit a higher extent of physical contact with the blood vessels. These dynamic responses of perivascular astrocytes and microglia are peaking at 4 days following LPS administration; however, they still persist at a lower level at 8 days after LPS injection, revealing incomplete reversal of inflammation affecting the glial properties and interactions within the NVU.

Astrocyte-neuron circuits in epilepsy

The epilepsies are a diverse spectrum of disease states characterized by spontaneous seizures and associated comorbidities. Neuron-focused perspectives have yielded an array of widely used anti-seizure medications and are able to explain some, but not all, of the imbalance of excitation and inhibition which manifests itself as spontaneous seizures. Furthermore, the rate of pharmacoresistant epilepsy remains high despite the regular approval of novel anti-seizure medications. Gaining a more complete understanding of the processes that turn a healthy brain into an epileptic brain (epileptogenesis) as well as the processes which generate individual seizures (ictogenesis) may necessitate broadening our focus to other cell types. As will be detailed in this review, astrocytes augment neuronal activity at the level of individual neurons in the form of gliotransmission and the tripartite synapse. Under normal conditions, astrocytes are essential to the maintenance of blood-brain barrier integrity and remediation of inflammation and oxidative stress, but in epilepsy these functions are impaired. Epilepsy results in disruptions in the way astrocytes relate to each other by gap junctions which has important implications for ion and water homeostasis. In their activated state, astrocytes contribute to imbalances in neuronal excitability due to their decreased capacity to take up and metabolize glutamate and an increased capacity to metabolize adenosine. Furthermore, due to their increased adenosine metabolism, activated astrocytes may contribute to DNA hypermethylation and other epigenetic changes that underly epileptogenesis. Lastly, we will explore the potential explanatory power of these changes in astrocyte function in detail in the specific context of the comorbid occurrence of epilepsy and Alzheimer's disease and the disruption in sleep-wake regulation associated with both conditions.

Role of aquaporins in corneal healing post chemical injury

Aquaporins (AQPs) are transmembrane water channel proteins that regulate the movement of water through the plasma membrane in various tissues including cornea. The cornea is avascular and has specialized microcirculatory mechanisms for homeostasis. AQPs regulate corneal hydration and transparency for normal vision. Currently, there are 13 known isoforms of AQPs that can be subclassified as orthodox AQPs, aquaglyceroporins (AQGPs), or supraquaporins (SAQPs)/unorthodox AQPs. AQPs are implicated in keratocyte function, inflammation, edema, angiogenesis, microvessel proliferation, and the wound-healing process in the cornea. AQPs play an important role in wound healing by facilitating the movement of corneal stromal keratocytes by squeezing through tight stromal matrix and narrow extracellular spaces to the wound site. Deficiency of AQPs can cause reduced concentration of hepatocyte growth factor (HGF) leading to reduced epithelial proliferation, reduced/impaired keratocyte migration, reduced number of keratocytes in the injury site, delayed and abnormal wound healing process. Dysregulated AQPs cause dysfunction in osmolar homeostasis as well as wound healing mechanisms. The cornea is a transparent avascular tissue that constitutes the anterior aspect of the outer covering of the eye and aids in two-thirds of visual light refraction. Being the outermost layer of the eye, the cornea is prone to injury. Of the 13 AQP isoforms, AQP1 is expressed in the stromal keratocytes and endothelial cells, and AQP3 and AQP5 are expressed in epithelial cells in the human cornea. AQPs can facilitate wound healing through aid in cellular migration, proliferation, migration, extracellular matrix (ECM) remodeling and autophagy mechanism. Corneal wound healing post-chemical injury requires an integrative and coordinated activity of the epithelium, stromal keratocytes, endothelium, ECM, and a battery of cytokines and growth factors to restore corneal transparency. If the chemical injury is mild, the cornea will heal with normal clarity, but severe injuries can lead to partial and/or permanent loss of corneal functions. Currently, the role of AQPs in corneal wound healing is poorly understood in the context of chemical injury. This review discusses the current literature and the role of AQPs in corneal homeostasis, wound repair, and potential therapeutic target for acute and chronic corneal injuries.

Administration of Kainic Acid Differentially Alters Astrocyte Markers and Transiently Enhanced Phospho-tau Level in Adult Rat Hippocampus

Kainic acid (KA), an analogue of the excitatory neurotransmitter glutamate, when administered systemically can trigger seizures and neuronal loss in a manner that mirrors the neuropathology of human mesial temporal lobe epilepsy (mTLE), which affects ∼50 million people globally. Evidence suggests that changes in astrocytes which precede neuronal damage play an important role in the degeneration of neurons and/or development of seizures in TLE pathogenesis. Additionally, a role for microtubule associated tau protein, involved in various neurodegenerative diseases including Alzheimer's disease, has also been suggested in the development of seizure and/or neurodegeneration in TLE pathogenesis. At present, possible alterations of different subtypes of astrocytes and their association, if any, with tau protein in TLE remain unclear. In this study, we evaluated alterations of different subtypes of astrocytes and phospho-/cleaved-tau levels in KA-treated rat model of TLE. Our results reveal that levels/expression of various astrocyte markers such as GFAP, vimentin, S100B, Aldh1L1, but not GS, are increased in the hippocampus of KA-treated rats. The levels/expression of both A1(C3+) and A2(S100A10+)-like astrocytes are also increased in KA-treated rats. Concurrently, the total (Tau1 and Tau5) and phospho-tau (AT270 and PHF1) levels are transiently enhanced following KA administration. Furthermore, the level/expression of cleaved-tau, which is apparent in a subset of GFAP-, S100B- and A2-positive astrocytes, are increased in KA-treated rats. These results, taken together, suggest a differential role for various astrocytic subpopulations and tau protein in the development of seizure and/or loss of neurons in KA model of TLE and possibly in human mTLE pathogenesis.

Regional variances depict a unique glial-specific inflammatory response following closed-head injury

Mild traumatic brain injuries (mTBI) constitute a significant health concern with clinical symptoms ranging from headaches to cognitive deficits. Despite the myriad of symptoms commonly reported following this injury, there is still a lack of knowledge on the various pathophysiological changes that occur. Preclinical studies are at the forefront of discovery delineating the changes that occur within this heterogeneous injury, with the emergence of translational models such as closed-head impact models allowing for further exploration of this injury mechanism. In the current study, male rats were subjected to a closed-head controlled cortical impact (cCCI), producing a concussion (mTBI). The pathological effects of this injury were then evaluated using immunoflourescence seven days following. The results exhibited a unique glial-specific inflammatory response, with both the ipsilateral and contralateral sides of the cortex and hippocampus showing pathological changes following impact. Overall these findings are consistent with glial changes reported following concussions and may contribute to subsequent symptoms.

Pre-existing Toxoplasma gondii infection increases susceptibility to pentylenetetrazol-induced seizures independent of traumatic brain injury in mice

Introduction

Post-traumatic epilepsy (PTE) is a debilitating chronic outcome of traumatic brain injury (TBI), and neuroinflammation is implicated in increased seizure susceptibility and epileptogenesis. However, how common clinical factors, such as infection, may modify neuroinflammation and PTE development has been understudied. The neurotropic parasite, Toxoplasma gondii (T. gondii) incurably infects one-third of the world's population. Thus, many TBI patients have a pre-existing T. gondii infection at the time of injury. T. gondii infection results in chronic low-grade inflammation and altered signaling pathways within the brain, and preliminary clinical evidence suggest that it may be a risk factor for epilepsy. Despite this, no studies have considered how a pre-existing T. gondii infection may alter the development of PTE.

Methods

This study aimed to provide insight into this knowledge gap by assessing how a pre-existing T. gondii infection alters susceptibility to, and severity of, pentylenetetrazol (PTZ)-induced seizures (i.e., a surrogate marker of epileptogenesis/PTE) at a chronic stage of TBI recovery. We hypothesized that T. gondii will increase the likelihood and severity of seizures following PTZ administration, and that this would occur in the presence of intensified neuroinflammation. To test this, 6-week old male and female C57BL/6 Jax mice were intraperitoneally injected with 50,000 T. gondii tachyzoites or with the PBS vehicle only. At 12-weeks old, mice either received a severe TBI via controlled cortical impact or sham injury. At 18-weeks post-injury, mice were administered 40 mg/kg PTZ and video-recorded for evaluation of seizure susceptibility. Fresh cortical tissue was then collected for gene expression analyses.

Results

Although no synergistic effects were evident between infection and TBI, chronic T. gondii infection alone had robust effects on the PTZ-seizure response and gene expression of markers related to inflammatory, oxidative stress, and glutamatergic pathways. In addition to this, females were more susceptible to PTZ-induced seizures than males. While TBI did not impact PTZ responses, injury effects were evident at the molecular level.

Discussion

Our data suggests that a pre-existing T. gondii infection is an important modifier of seizure susceptibility independent of brain injury, and considerable attention should be directed toward delineating the mechanisms underlying this pro-epileptogenic factor.

Aquaporins in Cardiovascular System

Recent studies have shown that aquaporins (AQPs) are involved in the regulation of cardiovascular function and the development of related diseases, especially in cerebral ischemia, congestive heart failure, hypertension, and angiogenesis. Therefore, further studies are needed to elucidate the mechanism accounting for the association between AQPs and vascular function-related diseases, which may lead to novel approaches to the prevention and treatment of those diseases. Here we will discuss the expression and physiological roles of AQPs in vascular tissues and summarize recent progress in the research on AQPs related cardiovascular diseases.

Reconnoitering the transformative journey of minocycline from an antibiotic to an antiepileptic drug

Minocycline, a second-generation tetracycline antibiotic is being widely tested in animals as well as clinical settings for the management of multiple neurological disorders. The drug has shown to exert protective action in a multitude of neurological disorders including spinal-cord injury, stroke, multiple sclerosis, amyotrophic lateral sclerosis, Huntington's disease, and Parkinson's disease. Being highly lipophilic, minocycline easily penetrates the blood brain barrier and is claimed to have excellent oral absorption (~100% bioavailability). Minocycline possesses anti-inflammatory, immunomodulatory, and anti-apoptotic properties, thereby supporting its use in treating neurological disorders. The article henceforth reviews all the recent advances in the transformation of this antibiotic into a potential antiepileptic/antiepileptogenic agent. The article also gives an account of all the clinical trials undertaken till now validating the antiepileptic potential of minocycline. Based on the reported studies, minocycline seems to be an important molecule for treating epilepsy. However, the practical therapeutic implementations of this molecule require extensive mechanism-based in-vitro (cell culture) and in-vivo (animal models) studies followed by its testing in randomized, placebo controlled and double-blind clinical trials in large population as well as in different form of epilepsies.

The role of aquaporin 4 (AQP4) in spinal cord injury

Aquaporin-4 (AQP-4) is an aquaporin composed of six helical transmembrane domains and two highly conserved ASN-pro-ALA (NPA) motifs. It is strongly expressed in rodent and human spinal cord tissues and plays a key role in the pathological process after SCI. After SCI, edema, glial scarring, and inflammation can accelerate the progression of injury and lead to deterioration of function. Many studies have reported that AQP-4 plays an important role in SCI. In particular, it plays an important role in secondary pathological processes (spinal cord edema, glial scar formation, and inflammatory response) after SCI. Loss of AQP-4 has been associated with reduced spinal edema and improved prognosis after SCI in mice. In addition, downregulation of AQP-4 reduces glial scar formation and the inflammatory response after SCI. There is a consensus from numerous studies that AQP-4 may be a potential target for SCI therapy, which guides the ongoing investigation for molecular therapy of SCI. Here, we review the structure of AQP-4, its expression in normal and damaged spinal cord, and its role in SCI, as well as discuss the theoretical basis for the treatment of SCI.

A clinical primer for the glymphatic system

The complex and dynamic system of fluid flow through the perivascular and interstitial spaces of the central nervous system has new-found implications for neurological diseases. Cerebrospinal fluid movement throughout the CNS parenchyma is more dynamic than could be explained via passive diffusion mechanisms alone. Indeed, a semi-structured glial-lymphatic (glymphatic) system of astrocyte-supported extracellular perivascular channels serves to directionally channel extracellular fluid, clearing metabolites and peptides to optimize neurologic function. Clinical studies of the glymphatic network has to date proven challenging, with most data gleaned from rodent models and post-mortem investigations. However, increasing evidence suggests that disordered glymphatic function contributes to the pathophysiology of CNS aging, neurodegenerative disease, and CNS injuries, as well as normal pressure hydrocephalus. Unlocking such pathophysiology could provide important avenues toward novel therapeutics. We here provide a multidisciplinary overview of glymphatics and critically review accumulating evidence regarding its structure, function, and hypothesized relevance to neurological disease. We highlight emerging technologies of relevance to the longitudinal evaluation of glymphatic function in health and disease. Finally, we discuss the translational opportunities and challenges of studying glymphatic science.

Astrocytes in the Traumatic Brain Injury: the Good and the Bad

Astrocytes control many processes of the nervous system in health and disease, and respond to injury quickly. Astrocytes produce neuroprotective factors in the injured brain to clear cellular debris and to orchestrate neurorestorative processes that are beneficial for neurological recovery after traumatic brain injury (TBI). However, astrocytes also become dysregulated and produce cytotoxic mediators that hinder CNS repair by induction of neuronal dysfunction and cell death. Hence, we discuss the potential role of astrocytes in neuropathological processes such as neuroinflammation, neurogenesis, synaptogenesis and blood-brain barrier repair after TBI. Thus, an improved understanding of the dual role of astrocytes may advance our knowledge of post-brain injury recovery, and provide opportunities for the development of novel therapeutic strategies for TBI.

Silencing of circIgf1r plays a protective role in neuronal injury via regulating astrocyte polarization during epilepsy

Epilepsy is a common brain disorder, repeated seizures of epilepsy may lead to a series of brain pathological changes such as neuronal or glial damage. However, whether circular RNAs are involved in neuronal injury during epilepsy is not fully understood. Here, we screened circIgf1r in the status epilepticus model through circRNA sequencing, and found that it was upregulated after the status epilepticus model through QPCR analysis. Astrocytes polarizing toward neurotoxic A1 phenotype and neurons loss were observed after status epilepticus. Through injecting circIgf1r siRNA into the lateral ventricle, it was found that knocking down circIgf1r in vivo would induce the polarization of astrocytes to phenotype A2 and reduce neuronal loss. The results in vitro further confirmed that inhibiting the expression of circIgf1r in astrocytes could protect neurons by converting reactive astrocytes from A1 to the protective A2. In addition, knocking down circIgf1r in astrocytes could functionally promote astrocyte autophagy and relieve the destruction of 4-AP-induced autophagy flux. In terms of mechanism, circIgf1r promoted the polarization of astrocytes to phenotype A1 by inhibiting autophagy. Taken together, our results reveal circIgf1r may serve as a potential target for the prevention and treatment of neuron damage after epilepsy.

N-Glycanase 1 Transcriptionally Regulates Aquaporins Independent of Its Enzymatic Activity

Patients with pathogenic mutations in NGLY1 cannot make tears and have global developmental delay and liver dysfunction. Traditionally, NGLY1 cleaves intact N-glycans from misfolded, retrotranslocated glycoproteins before proteasomal degradation. We demonstrate that Ngly1-null mouse embryonic fibroblasts, NGLY1 knockout human cells, and patient fibroblasts are resistant to hypotonic lysis. Ngly1-deficient mouse embryonic fibroblasts swell slower and have reduced aquaporin1 mRNA and protein expression. Ngly1 knockdown and overexpression confirms that Ngly1 regulates aquaporin1 and hypotonic cell lysis. Patient fibroblasts and NGLY1 knockout cells show reduced aquaporin11 mRNA, supporting NGLY1 as regulating expression of multiple aquaporins across species. Complementing Ngly1-deficient cells with catalytically inactive NGLY1 (p.Cys309Ala) restores normal hypotonic lysis and aquaporin1 protein. We show that transcription factors Atf1/Creb1 regulate aquaporin1 and that the Atf1/Creb1 signaling pathway is disrupted in Ngly1-deficient mouse embryonic fibroblasts. These results identify a non-enzymatic, regulatory function of NGLY1 in aquaporin transcription, possibly related to alacrima and neurological symptoms.

Neuroinflammatory mechanisms of post-traumatic epilepsy

BACKGROUND

Traumatic brain injury (TBI) occurs in as many as 64-74 million people worldwide each year and often results in one or more post-traumatic syndromes, including depression, cognitive, emotional, and behavioral deficits. TBI can also increase seizure susceptibility, as well as increase the incidence of epilepsy, a phenomenon known as post-traumatic epilepsy (PTE). Injury type and severity appear to partially predict PTE susceptibility. However, a complete mechanistic understanding of risk factors for PTE is incomplete.

MAIN BODY

From the earliest days of modern neuroscience, to the present day, accumulating evidence supports a significant role for neuroinflammation in the post-traumatic epileptogenic progression. Notably, substantial evidence indicates a role for astrocytes, microglia, chemokines, and cytokines in PTE progression. Although each of these mechanistic components is discussed in separate sections, it is highly likely that it is the totality of cellular and neuroinflammatory interactions that ultimately contribute to the epileptogenic progression following TBI.

CONCLUSION

This comprehensive review focuses on the neuroinflammatory milieu and explores putative mechanisms involved in the epileptogenic progression from TBI to increased seizure-susceptibility and the development of PTE.

Post-Traumatic Epilepsy and Seizure Susceptibility in Rat Models of Penetrating and Closed-Head Brain Injury

Traumatic brain injury (TBI) carries a risk of developing post-traumatic epilepsy (PTE). Currently, animal models that replicate clinical PTE (delayed spontaneous and recurrent seizures) are limited, which hinders pre-clinical research. In this study, we used two rat models of penetrating ballistic-like brain injury (PBBI) and closed-head injury (CHI) to induce spontaneous seizures and also measure changes in seizure susceptibility. In the PBBI model, two trajectories (frontal and lateral) and two injury severities for each trajectory, were evaluated. In the CHI model, a single projectile impact to the dorsal/lateral region of the head was tested. Continuous video-electroencephalographic (EEG) recordings were collected for 10 days at 1 or 6 month(s) post-injury. After EEG recording, all rats were given a sub-convulsant dose of pentylenetetrazole (PTZ) to challenge the seizure susceptibility. The video-EEG recording did not detect PTE following the PBBI. Only one CHI rat demonstrated persistent and recurrent non-convulsive seizures detected at 6 months post-injury. However, after PTZ challenge, 50-100% of the animals across different TBI groups experienced seizures. Seizure susceptibility increased over time from 1 to 6 months post-injury across the majority of TBI groups. Injury severity effects were not apparent within the PBBI model, but were evident between PBBI and CHI models. These results demonstrated the difficulties in detecting delayed spontaneous post-traumatic seizures even in a high-risk model of penetrating brain injury. The PTZ-induced increase in seizure susceptibility indicated the existence of vulnerable risk of epileptogenesis following TBI, which may be considered as an alternative research tool for pre-clinical studies of PTE.

[Reactive changes in morphological and morphometric parameters of immunopositive astrocytes of the amygdala in response to hormone level in absence epilepsy]

AIM

To study the changes in the morphological and morphometric parameters of immunopositive astrocytes of the amygdala in absence epilepsy depending on hormonal profile.

MATERIAL AND METHODS

Adult female WAG/Rij rats were used as experimental subjects. The astrocytes were detected on serial sections using a reaction to glial fibrillary acidic protein (GFAP) with pre-stained hematoxylin. Quantitative analysis was carried out for a 204.8´153.6 μm² field of view.

RESULTS

In the control group, astrocytes had a relatively regular stellate form and GFAP was moderately expressed in their bodies and processes. The number of astrocytes was 18.20±2.87, and their area was 164±3.29 μm². After ovariectomy, a high expression of the protein, both in the bodies and in the processes of astrocytes, increasing the cell size to 188.85±4.97 μm² (p<0.05) was observed. The astrocytes increased to 34.55±3.03 (p<0.05). In addition, the deformation of the processes and their diffuse defibration were observed. After hormone replacement therapy, a decrease in GFAP expression was detected, the area of astrocytes became smaller in comparison with the group after ovariectomy: 173.54±5.48 μm² (p<0.05). Morphological changes in glial cells were manifested as a decrease in the size of their bodies, the processes became smooth without diffuse sprouting and swelling, which is probably associated with neuroprotective functions of estradiol.

CONCLUSION

Thus, the results of our study demonstrated that the deficiency of female sex hormones led to the increase in both the amount and area of astrocytes in the anterior cortical nucleus of the amygdala, and hormone replacement therapy positively affected the structural and quantitative characteristics of astrocytes due to the endogenous protective role of estradiol.

TGN-020 alleviates edema and inhibits astrocyte activation and glial scar formation after spinal cord compression injury in rats

AIMS

Identifying drugs that inhibit edema and glial scar formation and increase neuronal survival is crucial to improving outcomes after spinal cord injury (SCI). Here, we used 2-(nicotinamide)-1,3,4-thiadiazole (TGN-020), a potent selective inhibitor of aquaporin 4 (AQP4), to investigate the effects of TGN-020 on SCI in Sprague-Dawley rats.

MAIN METHODS

We compressed the spinal cord at T10 using a sterile impounder (35 g, 5 min), to induce moderate injury. TGN-020 (100 mg/kg) or an equal volume of 10% dimethyl sulfoxide was then administered via intraperitoneal injection. Neurological function was evaluated using the Basso-Beattie-Bresnahan open-field locomotor scale 1, 3, 7, 14, 21, and 28 days after SCI. The degree of edema was assessed via determination of the precise spinal cord water content 3 days after SCI. Expression levels of AQP4, glial fibrillary acidic protein (GFAP), proliferating cell nuclear antigen (PCNA), and growth-associated protein-43 (GAP-43) were determined via western blotting and immunofluorescence staining 3 days after SCI and 4 weeks after SCI. Numbers of surviving neurons and glial scar sizes were determined using Nissl and hematoxylin-eosin staining, respectively.

KEY FINDINGS

Our results showed that TGN-020 promoted functional recovery at days 3, 7, 14, 21, and 28, as well as reduced the degree of edema and inhibited the expression of AQP4, GFAP, PCNA at days 3 after SCI. Furthermore, observations 4 weeks after SCI revealed that TGN-020 inhibited the glial scar formation and upregulated GAP-43 expression.

SIGNIFICANCE

TGN-020 can alleviate spinal cord edema, inhibit glial scar formation, and promote axonal regeneration, conferring beneficial effects on recovery in rats.

Inhibitory role of lentivirus-mediated aquaporin-4 gene silencing in the formation of glial scar in a rat model of traumatic brain injury

Traumatic brain injury (TBI), an acute degenerative pathology of the central nervous system, is a leading cause of death and disability. As the glial scar is a mechanical barrier to nerve regeneration, inhibitory molecules in the forming scar and methods to overcome them have suggested molecular modification strategies to allow neuronal growth and functional regeneration. Herein, we aim to investigate the effects of aquaporin-4 (AQP4) gene silencing on the glial scar formation after TBI by establishing rat models. After modeling, TBI rats were transfected with AQP4 small hairpin RNA [shRNA] (AQP4 gene silencing by lentiviral vector-delivered shRNA) and empty vectors, respectively. Neurological functions of the rats were evaluated after TBI. The hematoxylin and eosin staining was conducted to observe histomorphological changes in rat brain tissues. The messenger RNA (mRNA) and protein expressions of glial fibrillary acidic protein (GFAP), vimentin, fibronectin, laminin, and AQP4 were measured by reverse transcription-quantitative polymerase chain reaction and Western blot analysis. The ratio of positive expression area was calculated, and the glial scar was observed by immunohistochemistry. At the 7th, 14th, and 28th days after TBI, TBI rats treated with AQP4 shRNA showed improved neurological function and lessened histomorphological changes. AQP4 gene silencing mediated by lentivirus decreased the mRNA and protein expressions of GFAP, vimentin, fibronectin, and laminin, the number of positive cells, the ratio of positive expression area, and the glial scar. Our study demonstrates that lentivirus-mediated AQP4 gene silencing could inhibit the formation of glial scar after TBI, which is beneficial to the recovery of neurological function.

Astroglial role in the pathophysiology of status epilepticus: an overview

Status epilepticus is a medical emergency with elevated morbidity and mortality rates, and represents a leading cause of epilepsy-related deaths. Though status epilepticus can occur at any age, it manifests more likely in children and elderly people. Despite the common prevalence of epileptic disorders, a complete explanation for the mechanisms leading to development of self-limited or long lasting seizures (as in status epilepticus) are still lacking. Apart from neurons, research evidence suggests the involvement of immune and glial cells in epileptogenesis. Among glial cells, astrocytes represent an ideal target for the study of the pathophysiology of status epilepticus, due to their key role in homeostatic balance of the central nervous system. During status epilepticus, astroglial cells are activated by the presence of cytokines, damage associated molecular patterns and reactive oxygen species. The persistent activation of astrocytes leads to a decrease in glutamate clearance with a corresponding accumulation in the synaptic extracellular space, increasing the chance of neuronal excitotoxicity. Moreover, major alterations in astrocytic gap junction coupling, inflammation and receptor expression, facilitate the generation of seizures. Astrocytes are also involved in dysregulation of inhibitory transmission in the central nervous system and directly participate in ionic homeostatic alterations during status epilepticus. In the present review, we focus on the functional and structural changes in astrocytic activity that participate in the development and maintenance of status epilepticus, with special attention on concurrent inflammatory alterations. We also include potential astrocytic treatment targets for status epilepticus.

Regulation of cerebrospinal fluid (CSF) flow in neurodegenerative, neurovascular and neuroinflammatory disease

Cerebrospinal fluid (CSF) circulation and turnover provides a sink for the elimination of solutes from the brain interstitium, serving an important homeostatic role for the function of the central nervous system. Disruption of normal CSF circulation and turnover is believed to contribute to the development of many diseases, including neurodegenerative conditions such as Alzheimer's disease, ischemic and traumatic brain injury, and neuroinflammatory conditions such as multiple sclerosis. Recent insights into CSF biology suggesting that CSF and interstitial fluid exchange along a brain-wide network of perivascular spaces termed the 'glymphatic' system suggest that CSF circulation may interact intimately with glial and vascular function to regulate basic aspects of brain function. Dysfunction within this glial vascular network, which is a feature of the aging and injured brain, is a potentially critical link between brain injury, neuroinflammation and the development of chronic neurodegeneration. Ongoing research within this field may provide a powerful new framework for understanding the common links between neurodegenerative, neurovascular and neuroinflammatory disease, in addition to providing potentially novel therapeutic targets for these conditions. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Systemic inflammation in early neonatal mice induces transient and lasting neurodegenerative effects

Background

The inflammatory mediator lipopolysaccharide (LPS) has been shown to induce acute gliosis in neonatal mice. However, the progressive effects on the murine neurodevelopmental program over the week that follows systemic inflammation are not known. Thus, we investigated the effects of repeated LPS administration in the first postnatal week in mice, a condition mimicking sepsis in late preterm infants, on the developing central nervous system (CNS).

Methods

Systemic inflammation was induced by daily intraperitoneal administration (i.p.) of LPS (6 mg/kg) in newborn mice from postnatal day (PND) 4 to PND6. The effects on neurodevelopment were examined by staining the white matter and neurons with Luxol Fast Blue and Cresyl Violet, respectively. The inflammatory response was assessed by quantifying the expression/activity of matrix metalloproteinases (MMP), toll-like receptor (TLR)-4, high mobility group box (HMGB)-1, and autotaxin (ATX). In addition, B6 CX3CR1^gfp/+ mice combined with cryo-immunofluorescence were used to determine the acute, delayed, and lasting effects on myelination, microglia, and astrocytes.

Results

LPS administration led to acute body and brain weight loss as well as overt structural changes in the brain such as cerebellar hypoplasia, neuronal loss/shrinkage, and delayed myelination. The impaired myelination was associated with alterations in the proliferation and differentiation of NG2 progenitor cells early after LPS administration, rather than with excessive phagocytosis by CNS myeloid cells. In addition to disruptions in brain architecture, a robust inflammatory response to LPS was observed. Quantification of inflammatory biomarkers revealed decreased expression of ATX with concurrent increases in HMGB1, TLR-4, and MMP-9 expression levels. Acute astrogliosis (GFAP⁺ cells) in the brain parenchyma and at the microvasculature interface together with parenchymal microgliosis (CX3CR1⁺ cells) were also observed. These changes preceded the migration/proliferation of CX3CR1⁺ cells around the vessels at later time points and the subsequent loss of GFAP⁺ astrocytes.

Conclusion

Collectively, our study has uncovered a complex innate inflammatory reaction and associated structural changes in the brains of neonatal mice challenged peripherally with LPS. These findings may explain some of the neurobehavioral abnormalities that develop following neonatal sepsis.

Impairment of glymphatic pathway function promotes tau pathology after traumatic brain injury

Traumatic brain injury (TBI) is an established risk factor for the early development of dementia, including Alzheimer's disease, and the post-traumatic brain frequently exhibits neurofibrillary tangles comprised of aggregates of the protein tau. We have recently defined a brain-wide network of paravascular channels, termed the "glymphatic" pathway, along which CSF moves into and through the brain parenchyma, facilitating the clearance of interstitial solutes, including amyloid-β, from the brain. Here we demonstrate in mice that extracellular tau is cleared from the brain along these paravascular pathways. After TBI, glymphatic pathway function was reduced by ∼60%, with this impairment persisting for at least 1 month post injury. Genetic knock-out of the gene encoding the astroglial water channel aquaporin-4, which is importantly involved in paravascular interstitial solute clearance, exacerbated glymphatic pathway dysfunction after TBI and promoted the development of neurofibrillary pathology and neurodegeneration in the post-traumatic brain. These findings suggest that chronic impairment of glymphatic pathway function after TBI may be a key factor that renders the post-traumatic brain vulnerable to tau aggregation and the onset of neurodegeneration.

Aquaporin and brain diseases

BACKGROUND

The presence of water channel proteins, aquaporins (AQPs), in the brain led to intense research in understanding the underlying roles of each of them under normal conditions and pathological conditions.

SCOPE OF REVIEW

In this review, we summarize some of the recent knowledge on the 3 main AQPs (AQP1, AQP4 and AQP9), with a special focus on AQP4, the most abundant AQP in the central nervous system.

MAJOR CONCLUSIONS

AQP4 was most studied in several brain pathological conditions ranging from acute brain injuries (stroke, traumatic brain injury) to the chronic brain disease with autoimmune neurodegenerative diseases. To date, no specific therapeutic agents have been developed to either inhibit or enhance water flux through these channels. However, experimental results strongly underline the importance of this topic for future investigation. Early inhibition of water channels may have positive effects in prevention of edema formation in brain injuries but at later time points during the course of a disease, AQP is critical for clearance of water from the brain into blood vessels.

GENERAL SIGNIFICANCE

Thus, AQPs, and in particular AQP4, have important roles both in the formation and resolution of edema after brain injury. The dual, complex function of these water channel proteins makes them an excellent therapeutic target. This article is part of a Special Issue entitled Aquaporins.

Involvement of aquaporin 4 in astrocyte function and neuropsychiatric disorders

Aquaporin 4 (AQP4) is the main water channel in the central nervous system (CNS) and specifically localized to astrocyte processes. Recent studies indicate that AQP4 regulates various biological functions of astrocytes, including maintaining CNS water balance, spatial buffering of extracellular potassium, calcium signal transduction, regulation of neurotransmission, synaptic plasticity, and adult neurogenesis, while under neuropathological conditions, AQP4 has a role in astrogliosis and proinflammatory cytokine secretion. In addition, accumulating evidence suggests that, besides cerebral edema, neuromyelitis optica and epilepsy, AQP4 participates in the onset and progression of Alzheimer disease, Parkinson disease, depression, and drug addiction. This review summarizes recent findings and highlights the involvement of AQP4 in astrocyte function and neuropsychiatric disorders.

Novel frontiers in epilepsy treatments: preventing epileptogenesis by targeting inflammation

Currently available epilepsy drugs only affect the symptoms (seizures), and there is a need for innovative treatments that target the underlying disease. Increasing evidence points to inflammation as a potentially important mechanism in epileptogenesis. In the last decade, a new generation of etiologically realistic syndrome-specific experimental models have been developed, which are expected to capture the epileptogenic mechanisms operating in corresponding patient populations, and to exhibit similar treatment responsiveness. Recently, an intervention known to have broad-ranging anti-inflammatory effects (selective brain cooling) has been found to prevent the development of spontaneously occurring seizures in an etiologically realistic rat model of post-traumatic epilepsy. Several drugs used clinically for other indications also have the potential for inhibiting inflammation, and should be investigated for antiepileptogenic activity in these models. If results of such studies are positive, these compounds could rapidly enter Phase III trials in patients at high risk of developing epilepsy.

Aquaporin-4 mitigates retrograde degeneration of rubrospinal neurons by facilitating edema clearance and glial scar formation after spinal cord injury in mice

Atrophy of upper motor neurons hampers axonal regeneration and functional recovery following spinal cord injury (SCI). Apart from the severity of primary injury, a series of secondary pathological damages including spinal cord edema and glial scar formation affect the fate of injured upper motor neurons. The aquaporin-4 (AQP4) water channel plays a critical role in water homeostasis and migration of astrocytes in the central nervous system, probably offering a new therapeutic target for protecting against upper motor neuron degeneration after SCI. To test this hypothesis, we examined the effect of AQP4 deficiency on atrophy of rubrospinal neurons after unilateral rubrospinal tract transection at the fourth cervical level in mice. AQP4 gene knockout (AQP4-/-) mice exhibited high extent of spinal cord edema at 72 h after lesion compared with wild-type littermates. AQP4-/- mice showed impairments in astrocyte migration toward the transected site with a greater lesion volume at 1 week after surgery and glial scar formation with a larger cyst volume at 6 weeks. More severe atrophy and loss of axotomized rubrospinal neurons as well as axonal degeneration in the rubrospinal tract rostral to the lesion were observed in AQP4-/- mice at 6 weeks after SCI. AQP4 expression was downregulated at the lesioned spinal segment at 3 days and 1 week after injury, but upregulated at 6 weeks. These results demonstrated that AQP4 not only mitigates spinal cord damage but also ameliorates retrograde degeneration of rubrospinal neurons by promoting edema clearance and glial scar formation after laceration SCI. This finding supports the notion that AQP4 may be a promising therapeutic target for SCI.

Bridge between neuroimmunity and traumatic brain injury

The pathophysiology of degenerative, infectious, inflammatory and traumatic diseases of the central nervous system includes a significant immune component. As to the latter, damage to the cerebral vasculature and neural cell bodies, caused by traumatic brain injury (TBI) activates innate immunity with concomitant infiltration of immunocytes into the damaged nervous system. This leads to proinflammatory cytokine and prostaglandin production and lost synaptic integrity and more generalized neurotoxicity. Engagement of adaptive immune responses follows including the production of antibodies and lymphocyte proliferation. These affect the tempo of disease along with tissue repair and as such provide a number of potential targets for pharmacological treatments for TBI. However, despite a large body of research, no such treatment intervention is currently available. In this review we will discuss the immune response initiated following brain injuries, drawing on knowledge gained from a broad array of experimental and clinical studies. Our discussion seeks to address potential therapeutic targets and propose ways in which the immune system can be controlled to promote neuroprotection.

Traumatic Brain Injury pathophysiology and treatments: early, intermediate, and late phases post-injury

Traumatic Brain Injury (TBI) affects a large proportion and extensive array of individuals in the population. While precise pathological mechanisms are lacking, the growing base of knowledge concerning TBI has put increased emphasis on its understanding and treatment. Most treatments of TBI are aimed at ameliorating secondary insults arising from the injury; these insults can be characterized with respect to time post-injury, including early, intermediate, and late pathological changes. Early pathological responses are due to energy depletion and cell death secondary to excitotoxicity, the intermediate phase is characterized by neuroinflammation and the late stage by increased susceptibility to seizures and epilepsy. Current treatments of TBI have been tailored to these distinct pathological stages with some overlap. Many prophylactic, pharmacologic, and surgical treatments are used post-TBI to halt the progression of these pathologic reactions. In the present review, we discuss the mechanisms of the pathological hallmarks of TBI and both current and novel treatments which target the respective pathways.

Traumatic scratch injury in astrocytes triggers calcium influx to activate the JNK/c-Jun/AP-1 pathway and switch on GFAP expression

Astrocyte activation is a hallmark of central nervous system injuries resulting in glial scar formation (astrogliosis). The activation of astrocytes involves metabolic and morphological changes with complex underlying mechanisms, which should be defined to provide targets for astrogliosis intervention. Astrogliosis is usually accompanied by an upregulation of glial fibrillary acidic protein (GFAP). Using an in vitro scratch injury model, we scratched primary cultures of cerebral cortical astrocytes and observed an influx of calcium in the form of waves spreading away from the wound through gap junctions. Using the calcium blocker BAPTA-AM and the JNK inhibitor SP600125, we demonstrated that the calcium wave triggered the activation of JNK, which then phosphorylated the transcription factor c-Jun to facilitate the binding of AP-1 to the GFAP gene promoter to switch on GFAP upregulation. Blocking calcium mobilization with BAPTA-AM in an in vivo stab wound model reduced GFAP expression and glial scar formation, showing that the calcium signal, and the subsequent regulation of downstream signaling molecules, plays an essential role in brain injury response. Our findings demonstrated that traumatic scratch injury to astrocytes triggered a calcium influx from the extracellular compartment and activated the JNK/c-Jun/AP-1 pathway to switch on GFAP expression, identifying a previously unreported signaling cascade that is important in astrogliosis and the physiological response following brain injury.

Posttraumatic reduction of edema with aquaporin-4 RNA interference improves acute and chronic functional recovery

Traumatic brain injury (TBI) is common in young children and adolescents and is associated with long-term disability and mortality. The neuropathologic sequelae that result from juvenile TBI are a complex cascade of events that include edema formation and brain swelling. Brain aquaporin-4 (AQP4) has a key role in edema formation. Thus, development of novel treatments targeting AQP4 to reduce edema could lessen the neuropathologic sequelae. We hypothesized that inhibiting AQP4 expression by injection of small-interfering RNA (siRNA) targeting AQP4 (siAQP4) after juvenile TBI would decrease edema formation, neuroinflammation, neuronal cell death, and improve neurologic outcomes. The siAQP4 or a RNA-induced silencing complex (RISC)-free control siRNA (siGLO) was injected lateral to the trauma site after controlled cortical impact in postnatal day 17 rats. Magnetic resonance imaging, neurologic testing, and immunohistochemistry were performed to assess outcomes. Pups treated with siAQP4 showed acute (3 days after injury) improvements in motor function and in spatial memory at long term (60 days after injury) compared with siGLO-treated animals. These improvements were associated with decreased edema formation, increased microglial activation, decreased blood-brain barrier disruption, reduced astrogliosis and neuronal cell death. The effectiveness of our treatment paradigm was associated with a 30% decrease in AQP4 expression at the injection site.

Combined SCI and TBI: recovery of forelimb function after unilateral cervical spinal cord injury (SCI) is retarded by contralateral traumatic brain injury (TBI), and ipsilateral TBI balances the effects of SCI on paw placement

A significant proportion (estimates range from 16 to 74%) of patients with spinal cord injury (SCI) have concomitant traumatic brain injury (TBI), and the combination often produces difficulties in planning and implementing rehabilitation strategies and drug therapies. For example, many of the drugs used to treat SCI may interfere with cognitive rehabilitation, and conversely drugs that are used to control seizures in TBI patients may undermine locomotor recovery after SCI. The current paper presents an experimental animal model for combined SCI and TBI to help drive mechanistic studies of dual diagnosis. Rats received a unilateral SCI (75 kdyn) at C5 vertebral level, a unilateral TBI (2.0 mm depth, 4.0 m/s velocity impact on the forelimb sensori-motor cortex), or both SCI+TBI. TBI was placed either contralateral or ipsilateral to the SCI. Behavioral recovery was examined using paw placement in a cylinder, grooming, open field locomotion, and the IBB cereal eating test. Over 6weeks, in the paw placement test, SCI+contralateral TBI produced a profound deficit that failed to recover, but SCI+ipsilateral TBI increased the relative use of the paw on the SCI side. In the grooming test, SCI+contralateral TBI produced worse recovery than either lesion alone even though contralateral TBI alone produced no observable deficit. In the IBB forelimb test, SCI+contralateral TBI revealed a severe deficit that recovered in 3 weeks. For open field locomotion, SCI alone or in combination with TBI resulted in an initial deficit that recovered in 2 weeks. Thus, TBI and SCI affected forelimb function differently depending upon the test, reflecting different neural substrates underlying, for example, exploratory paw placement and stereotyped grooming. Concurrent SCI and TBI had significantly different effects on outcomes and recovery, depending upon laterality of the two lesions. Recovery of function after cervical SCI was retarded by the addition of a moderate TBI in the contralateral hemisphere in all tests, but forepaw placements were relatively increased by an ipsilateral TBI relative to SCI alone, perhaps due to the dual competing injuries influencing the use of both forelimbs. These findings emphasize the complexity of recovery from combined CNS injuries, and the possible role of plasticity and laterality in rehabilitation, and provide a start towards a useful preclinical model for evaluating effective therapies for combine SCI and TBI.

'Hit & Run' model of closed-skull traumatic brain injury (TBI) reveals complex patterns of post-traumatic AQP4 dysregulation

Cerebral edema is a major contributor to morbidity associated with traumatic brain injury (TBI). The methods involved in most rodent models of TBI, including head fixation, opening of the skull, and prolonged anesthesia, likely alter TBI development and reduce secondary injury. We report the development of a closed-skull model of murine TBI, which minimizes time of anesthesia, allows the monitoring of intracranial pressure (ICP), and can be modulated to produce mild and moderate grade TBI. In this model, we characterized changes in aquaporin-4 (AQP4) expression and localization after mild and moderate TBI. We found that global AQP4 expression after TBI was generally increased; however, analysis of AQP4 localization revealed that the most prominent effect of TBI on AQP4 was the loss of polarized localization at endfoot processes of reactive astrocytes. This AQP4 dysregulation peaked at 7 days after injury and was largely indistinguishable between mild and moderate grade TBI for the first 2 weeks after injury. Within the same model, blood-brain barrieranalysis of variance permeability, cerebral edema, and ICP largely normalized within 7 days after moderate TBI. These findings suggest that changes in AQP4 expression and localization may not contribute to cerebral edema formation, but rather may represent a compensatory mechanism to facilitate its resolution.

Cognitive and cerebrovascular improvements following kinin B1 receptor blockade in Alzheimer's disease mice

Background

Recent evidence suggests that the inducible kinin B₁ receptor (B₁R) contributes to pathogenic neuroinflammation induced by amyloid-beta (Aβ) peptide. The present study aims at identifying the cellular distribution and potentially detrimental role of B₁R on cognitive and cerebrovascular functions in a mouse model of Alzheimer’s disease (AD).

Methods

Transgenic mice overexpressing a mutated form of the human amyloid precursor protein (APP_Swe,Ind, line J20) were treated with a selective and brain penetrant B₁R antagonist (SSR240612, 10 mg/kg/day for 5 or 10 weeks) or vehicle. The impact of B₁R blockade was measured on i) spatial learning and memory performance in the Morris water maze, ii) cerebral blood flow (CBF) responses to sensory stimulation using laser Doppler flowmetry, and iii) reactivity of isolated cerebral arteries using online videomicroscopy. Aβ burden was quantified by ELISA and immunostaining, while other AD landmarks were measured by western blot and immunohistochemistry.

Results

B₁R protein levels were increased in APP mouse hippocampus and, prominently, in reactive astrocytes surrounding Aβ plaques. In APP mice, B₁R antagonism with SSR240612 improved spatial learning, memory and normalized protein levels of the memory-related early gene Egr-1 in the dentate gyrus of the hippocampus. B₁R antagonism restored sensory-evoked CBF responses, endothelium-dependent dilations, and normalized cerebrovascular protein levels of endothelial nitric oxide synthase and B₂R. In addition, SSR240612 reduced (approximately 50%) microglial, but not astroglial, activation, brain levels of soluble Aβ_1-42, diffuse and dense-core Aβ plaques, and it increased protein levels of the Aβ brain efflux transporter lipoprotein receptor-related protein-1 in cerebral microvessels.

Conclusion

These findings show a selective upregulation of astroglial B₁R in the APP mouse brain, and the capacity of the B₁R antagonist to abrogate amyloidosis, cerebrovascular and memory deficits. Collectively, these findings provide convincing evidence for a role of B₁R in AD pathogenesis.

Aquaporin 4: a player in cerebral edema and neuroinflammation

Neuroinflammation is a common pathological event observed in many different brain diseases, frequently associated with blood brain barrier (BBB) dysfunction and followed by cerebral edema. Neuroinflammation is characterized with microglia activation and astrogliosis, which is a hypertrophy of the astrocytes. Astrocytes express aquaporin 4, the water channel protein, involved in water homeostasis and edema formation. Aside from its function in water homeostasis, recent studies started to show possible interrelations between aquaporin 4 and neuroinflammation. In this review the roles of aquaporin 4 in neuroinflammation associated with BBB disruption and cerebral edema will be discussed with recent studies in the field.

Different aquaporin-4 expression in glioblastoma multiforme patients with and without seizures

Aquaporin-4 (AQP-4), the most important water channel in the brain, is expressed by astrocyte end feet abutting microvessels. Altered expression levels of AQP-4 and redistribution of the protein throughout the membranes of cells found in glioblastoma multiforme (GBM) lead to development of the edema often found surrounding the tumor mass. Dysregulation of AQP-4 also occurs in hippocampal sclerosis and cortical dysplasia in patients with refractory partial epilepsy. This work reports on analysis of the relationship between AQP-4 expression and the incidence of epileptic seizures in patients with GBM. Immunohistochemical and polymerase chain reaction techniques were used to evaluate AQP-4 in biopsy specimens from 19 patients with GBM, 10 of who had a history of seizures before surgery. AQP-4 mRNA levels were identical in the two groups of patients, but AQP-4 expression was more frequently detected on the GBM membranes from specimens of patients with seizures than from individuals without (10 versus 2, P < 0.001). We conclude that reduced expression of cell surface AQP-4 is characteristic of GBM patients without seizures, likely attributable to a posttranslational mechanism.

The mutation in Chd7 causes misexpression of Bmp4 and developmental defects in telencephalic midline

Mutations in chromosome-helicase-DNA-binding protein 7 (CHD7) are identified as the main cause for CHARGE syndrome (coloboma, heart anomaly, choanal atresia, retardation, genital and ear anomalies). Most patients (55% to 85%) with CHARGE syndrome display developmental defects in the central nervous system (CNS), of which pathology and molecular mechanisms remain unclear. In this study, we report a novel mutant mouse strain carrying a nonsense mutation, COA1, in exon4 of Chd7 gene. Chd7(COA1/+) mice phenocopied human CHARGE syndrome and displayed developmental defects in the telencephalic midline, including dilated third and lateral ventricles, reduced cerebral cortex, and corpus callosum crossing failure. Programed cell death in the telencephalic midline zone of Chd7(COA1/+) embryos was impaired, consistent with the incomplete telencephalic medial invagination in Chd7(COA1/+) embryos. Interestingly, expression of Bmp4, a signal well known to induce forebrain midline cell fate and apoptosis, was down-regulated and also expanded in the forebrain of Chd7(COA1/+) embryos. Furthermore, in vitro studies suggested that CHD7 may directly regulate Bmp4 expression by binding with an enhancer element downstream of the Bmp4 locus. These studies provide novel insight into pathogenesis of CNS anomalies in CHARGE syndrome.